Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
  • G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
  • G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
  • G01R19/16576—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing DC or AC voltage with one threshold
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
  • H03K3/02—Generators characterised by the type of circuit or by the means used for producing pulses
  • H03K3/353—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of field-effect transistors with internal or external positive feedback
  • H03K3/356—Bistable circuits
  • H03K3/3565—Bistables with hysteresis, e.g. Schmitt trigger

Definitions

• Input circuit for converting an input voltage into a binary
• the invention relates to an input circuit for converting an input voltage into a binary information signal, with an input current initially rising up to a predeterminable maximum value with increasing input voltage and falling again with a further increasing input voltage above a predefinable input voltage value and generating a binary output signal, the state of which is one direction changes when the input voltage exceeds a predefinable limit value, hereinafter referred to as the switch-on voltage, and changes in the other direction when the input voltage falls below this limit value or optionally a limit value lower by a hysteresis voltage.
• a predefinable limit value hereinafter referred to as the switch-on voltage
• This input circuit can be supplied with input voltages that are within a wide range. For example, nominal input voltages in the range of 0 to 300 V can be applied. Adjustment measures for the respective existing input voltage, which is within the range, are not necessary. There is often a requirement to provide electrical isolation.
• mains frequency 50, 60 Hz
• the nominal voltage ranges of the process signals are usually between 24 V and 230 V - in mobile systems (e.g. vehicles) also below.
• Which signal voltages (height, frequency) are used in a specific case depends on current requirements (energy sources: system voltage, vehicle electrical system ...; signal sources: sensors, sensors, relays ...; cable lengths, interference environment %), but also on the original enemies of the technology used (relay control technology, measurement technology, control technology, energy transmission technology, electrical engineering, vehicle controls, mining, shipbuilding ...) and the standards derived from it.
• With mechanical signal sources (encoders, relay contacts ...) a certain minimum current is often required for contact cleaning (e.g. 20 - 30 mA, at least when switched on).
• the current carrying capacity of a signal source has an upper limit. Components with different signal voltages often have to be combined in a system.
• Input circuits are also known, in which process signals are converted into a signal of the control logic in a separate SignaL matching circuit (Elektroni k 12 / 12.6, 1987, p. 146).
• the required immunity to interference is achieved in that the signal matching circuit can only be brought into the on-state by a signal source by applying a certain minimum power. This minimum power (interference power barrier) is selected so that it can only be generated by regular signal sources (useful signals) and not by interference coupling
• Interference signals can be applied (e.g. 500 mW).
• a large signal-to-noise ratio alone does not result in general immunity to interference, since it only protects against special interference signals.
• a disadvantage in connection with the power-related interference immunity is the fact that the required power is obtained as power loss in the signal matching circuit. Since the power loss in standard circuits increases approximately quadratically with the actual signal voltage (ohmic behavior), previously individually dimensioned matching circuits had to be used in order to find a compromise between the permissible values
• Adaptation circuit can be implemented with the simplest of means.
• the switching point would be chosen so that it is also the smallest
• Nominal voltage is even more safely below the value for on signals (e.g. 6 V).
• the circuit also had to make do with a relatively low input current via non-input voltages in order to rule out power loss problems. This leads to simple circuits with approximately ohmic input resistance to a relatively high input sensitivity. Unfortunately, a circuit designed in this way is much too susceptible to interference in practice, since even low interference energies cause impermissible changes in the state of the output signal.
• a matching circuit for a certain nominal voltage should have a certain interference power barrier. This is then also decisive for the lower limit of the power loss, which must at least be mastered by the matching circuit. If you put z. For example, if a matching circuit for 24-volt signals is used so that the breakpoint is 18 V and 30 mA (contact cleaning current), then a switching power of at least 540 mW must be applied to achieve the switch-on state. At the same time, this results in an immunity to interference of 540 mW, since interference signals that do not achieve this power cannot cause any changes. A prerequisite is that the switching point parameters are adhered to with sufficient accuracy. A dependence of the switching point on strongly scattering component parameters, such as. E. Transistor gain factors or highly aging dependent transmission factors from optocouplers should be avoided.
• Power loss of 960 mW can be controlled. With a signal voltage of 240 V, however, a power loss of 96 W (3) would occur in the matching circuit and would be released to the environment. Circuits that can withstand such power losses are very voluminous and expensive. A large number of matching circuits is usually required in a system, so that mastering the total power loss of the matching circuits would cause considerable (sometimes unsolvable) problems. To make matters worse, the energy and signal sources have to provide and switch these powers, which is not always feasible.
• Interference currents coupled in interference energy is not sufficient for switching, an additional interference (e.g. due to mains frequency interference) is often sufficient to exceed the switching point. This applies particularly to matching circuits whose input resistance is below the entire voltage range
• Switching threshold is relatively high resistance.
• the useful signal is an AC voltage signal (e.g. 50 Hz mains frequency)
• low-pass filters cannot protect against interference in this frequency range, since they also attenuate the useful signal.
• the adaptation to these conditions leads to considerable additional effort and corresponding costs in all areas that have to do with these products.
• the invention is based on the object of further developing an input circuit of the type described at the outset in such a way that it only responds when there is a predefinable interference power barrier, only when a predeterminable holding energy falls back below it, has a power loss limitation, is suitable for a nominal input voltage lying within a wide range and is suitable for a current picks up, which is higher before the response than at voltages far above the response voltage. Signals within the large nominal voltage range mentioned at the outset should therefore be processed.
• Adequate interference immunity is achieved at the interface between the process and control system due to the properties mentioned.
• a particularly important part of the task is that the
• Input circuit no supply voltage from an external operating voltage source required.
• the input circuit draws all of its energy required for its operation from the input voltage.
• a second electrical control element is provided in the second input circuit.
• the input circuit can be constructed in such a way that one of the two subcircuits contains the other in whole or in part.
• the subcircuits can be arranged entirely or partially in parallel or in series with one another.
• the second electrical control element preferably changes from the non-conductive to the conductive state when the input voltage exceeds the switching threshold. This results in a simple circuit structure.
• the second electrical control element can form the output of the input circuit. It is also possible that the second control element, without forming the output of the input circuit, a current (which is only a part of the
• Input current can be switched) and this current is an electrical one Flows through coupling element, which generates the binary output signal, the binary output signal being held in one state and otherwise in the other state when current flows through the coupling element.
• the current flowing through the second control element can be wholly, partially or not at all part of the current through the first electrical control element.
• the electrical coupling element can in principle be arranged at any point where it is essentially only from that through the second
• Control switched current will flow through.
• it is a resistor (the binary signal is formed by the voltage drop).
• Electromagnetic coupling elements are also possible.
• the current switched by the second control element can influence the current through the first control element directly or via an electrical network.
• the first control contains e.g. B. one or more control inputs.
• the network contains e.g. B. a third electrical control element.
• the influencing is such that when the current in the second control element is switched on and the binary output signal changes, the reduction in the input current by the first electrical control element begins.
• the current flowing through the second control element is limited to a predeterminable, in the simplest case constant value by wiring the second control element or by special circuit parts.
• the proportion of current flowing only through the first subcircuit preferably decreases to such an extent that it is above a predefinable one
• Input voltage limit becomes zero and the input current of the input circuit essentially only by the limited current in the second
• the input circuit can in particular contain a first current path which is acted upon by the input voltage and has a low-impedance at input voltages below the switch-on voltage and which contains at least one resistor in series with a first and a possible second transistor, at least the coupling-out element in series with a third transistor which is connected with input voltages has a high resistance below the switch-on voltage, forms a second current path that bridges the second transistor, the resistance of which increases with increasing input voltages, while the resistance of the third transistor is reduced, and the first transistor is set to constant current from an honing input voltage.
• An optocoupler with a pipo-phototransistor output is preferably provided as the decoupling element. This enables simple but very flexible adaptability to the circuit technology to be controlled. It can handle TTL levels, but also higher voltage levels.
• the V a l en z of the output signal is freely selectable. If you close z. B. the emitter at 0 V and applies the collector to a resistor at + 5 V, then there is a TTL signal, which is binary zero when the input signal is active. If you connect the collector directly to + 5 V and the emitter via a resistor to C V, you get a TTL signal in the other valence.
• a preferred embodiment consists in that the first transistor, which is designed as a depletion-type FET, with the drain electrode to a resistor acted upon by the input voltage and with the source electrode to the drain electrode of the second transistor and via a resistor with the Optocoupler is connected, which is followed by the drain electrode of the third transistor designed as an FET, which is connected with its source electrode to the other pole of the input voltage, de r via a resistor, the source electrode of the second transistor and a
• Resistance acts on the gate electrode of the third transistor, the gate electrode of which is connected via a further resistor to the source electrode of the first transistor and via an additional resistor to the drain electrode of the first transistor, that the gate electrode of the first transistor is connected to the optocoupler and that the gate electrode of the second transistor to the drain electrode of the oritten
• Transistor is connected. This arrangement has a characteristic, static current-voltage characteristic with hysteresis behavior and partially negative differential resistance.
• the arrangement has ohmic behavior at least above a low threshold voltage.
• the current increases proportionally with the voltage up to a switch-on voltage. Wind reaches the switch-on voltage, then the third transistor becomes conductive when its threshold voltage is exceeded, as a result of which the gate voltage of the second transistor drops and the latter becomes less conductive, ie the current through the transistor go back. After this switching, the current is still so high that a sufficiently high power is implemented with the associated input voltage.
• This power dissipation prevents interference voltages or interference currents from reversing the response of the arrangement, ie the valence of the output signal associated with the input voltage from zero to the response voltage occurs again. From the point at which the current jumps, a constant current flows through the luminescent diode of the optocoupler.
• the second transistor is controlled by the negative feedback described in the range of higher resistances until it is non-conductive at a certain input voltage. Following this, only the constant current flows through the arrangement at even higher voltages. The power loss then only increases proportionally with the part of the input voltage which is above this input voltage.
• the characteristic which is favorable in terms of interference sensitivity both before and after the input module responds for the entire range of the input voltage, is achieved by the circuit with three active components which are connected to one another in such a way that a feedback between the active components after the response voltage is reached the response is at least partially replaced by negative feedback.
• the characteristic curve roughly corresponds to a Hyberbel in a certain voltage range. A hyperbole would mean constant power loss. It can be approximated further by more complex positive and negative feedback networks, in particular using nonlinear components.
• Zener diodes In order to reduce the influence of the threshold voltage tolerances of the FETs on the characteristic curve, it is advisable to insert Zener diodes in the arrangement.
• a first zener diode is arranged between the gate electrode of the third transistor and the resistors which provide the gate potential.
• a second zener diode is located between the gate electrode of the first transistor and the anode of the luminescence diode of the optocoupler.
• a resistor is required to keep this Zener diode in the conductive state.
• the resistor is arranged between the gate electrode and the source electrode of the first transistor, can also with other points higher potentials.
• the first transistor can also be of the enhancement type.
• the use of the Zener diodes is independent of each other. each one already improves the effect of the circuit on its own.
• the Zener voltages are large compared to the threshold voltages of the transistors. The influence of the threshold voltages on the working points is thereby reduced.
• a resistor is connected in parallel to the luminescent diode of the optocoupler.
• the gate voltage at the third transistor is expediently limited using a Zener diode D.
• the third Zener diode is expediently connected in front of the optocoupler, so that the Zener current does not flow through the optocoupler.
• This current limitation eliminates the peak at the switching point in the characteristic curve, since the maximum current is reached beforehand and is maintained up to the switching point.
• Another possibility to give the input current this course is in the following variant: Instead of a resistor in the source circuit of the first transistor, two resistors are provided in series, the drain electrode of the second transistor being connected to the common connection point of the two resistors is.
• Gate-source threshold voltage is reached. From this point on, the first transistor limits the input current to the maximum value (Imax) that has just been reached. The current remains constant as the input voltage rises until the input voltage reaches the value of the switch-on voltage. Then the one already described also applies to this circuit variant
• the first transistor can also be an enhancement type MOSFET. So that this transistor becomes conductive when the input voltage is applied, is a Resistance is provided between the first input of the input module and the gate electrode of the first transistor. No resistance is then required between the gate and source electrodes. Otherwise, nothing changes compared to the arrangement described above. For some applications, the falling part after the jump in the characteristic curve after the response is not necessary. The resistance between the drain electrode of the first transistor and the gate electrode of the third transistor can then be eliminated. After the response, the first transistor then immediately carries a constant current. If you initially accept a very non-resistive curve at low input voltages below the switch-on voltage, then the second transistor in all its variants can be replaced by a Zener diode.
• 1 is a circuit diagram of an input circuit for converting an input voltage into a binary information signal
• Fig. 2 is a circuit diagram of a second input circuit for implementing a
• Fig. 3 is a diagram of the input circuits of FIG. 1 or 2 in
• Fig. 4 is a circuit diagram of a third input circuit for implementing a
• FIG. 5 shows a diagram of the current drawn by the input circuits according to FIG. 4 as a function of the input voltage
• Fig. 6 is a circuit diagram of a fourth input circuit for implementing a
• Fig. 7 is a circuit diagram of another input circuit for implementing a
• An input circuit for converting an input voltage into a binary information signal has two inputs 1, 2 which are applied to the input voltage.
• the input voltage is a DC voltage or a pulsating DC voltage. If AC voltages are rarely converted into binary signals, there is a between the AC voltage signal source and the inputs 1, 2
• Rectifier e.g. B. a bridge rectifier provided.
• the input circuit shown in FIG. 1 contains a first current path 3, which consists of a resistor 4 connected to the input 1 in series with a first transistor 5, a second transistor 6 and a resistor 7.
• the resistor 7 is connected to the second input 2.
• the two transistors 5, 6 are FETs.
• At least transistor 5 is a depletion type MOSFET transistor or a p-channel junction field effect transistor.
• the resistors 4, 7 are in the range up to a few hundred ohms.
• a second current path 8 runs parallel to the transistor 6 and the
• the second current path contains a resistor 9 in series with a luminescent diode 10 and a third transistor 11, which is also an FET.
• the transistor 11 is connected with the drain electrode to the luminescence diode 10 and to the gate electrode of the transistor 6.
• the source electrode of transistor 11 is connected to input 2.
• the transistor 11 is provided with a high-resistance resistor 12 between the gate and source electrodes.
• a resistor 13 is connected to the drain electrode of transistor 5 and is also connected to the gate electrode of transistor 11.
• a second high-resistance resistor 14 connects the source electrode of transistor 5 to the gate electrode of transistor 11.
• the gate electrode of transistor 5 is connected to the anode of the luminescent diode 10.
• the arrangement according to FIG. 1 can be constructed with FETs or bipolar transistors, inter alia also with complementary transistors.
• the transistor 5 is in a saturated state when an input voltage is applied, and only the gate-source threshold voltage drops at the transistor 6, since it works as a source follower whose gate voltage is initially at drain potential, as a result of which a low-resistance, conductive connection between inputs 1 and 2.
• the transistor 11 is
• Source electrode of the transistor 5 on which leads to a larger opening of the transistor 11 due to positive feedback.
• the transistor has suddenly become a negative feedback.
• the switch-on process is ended when the effect of the sudden negative feedback just compensates for the effect of the continued positive feedback that occurs via the resistor 13 lying between the drain electrode of the first transistor and the gate electrode of the third transistor.
• the input current then fell from the maximum value (B) to a small value (C) at the switch-on voltage. If the input voltage continues to increase, a linear current decrease is achieved by the positive feedback via the resistor 13 and by the negative feedback via the resistor 14 until the transistor 6 is completely blocked (point D in FIG. 3). From this point on, the current remains constant over an increasing input voltage (point E in FIG. 3). This is the current flowing through the optocoupler and transistor 11.
• the input circuit according to FIG. 1 allows the device to be operated with a wide variety of input signal nominal voltages (24 V ... 230 V, at
• Fig. 3 This is mainly achieved by the special shape of the input characteristic, which is shown in Fig. 3.
• the input voltage applied to the input circuit is shown in the abscissa direction and the current consumed by the input circuit is shown in the ordinate direction.
• the resulting characteristic has a continuation.
• Fig. 3 only part of the characteristic static current-voltage characteristic of the input circuit is shown, namely for positive input voltages.
• the continuation of the characteristic curve is obtained by rotating the input signal curve at the zero point by 180 degrees in the 3rd quadrant and mirroring the output characteristic curve on the "current axis".
• the behavior of the input circuit means that the polarity of the input signal is irrelevant.
• the module can also be used with AC signals.
• the course of the characteristic curves shows that the circuit has a hysteresis behavior.
• the individual curve sections are normally reversed. Only the vertical curve parts can only be traversed in the direction of the direction arrows drawn there.
• the input voltage axis is for both the input current curve and the
• Each point in the output status curve identified by a letter with an apostrophe is matched by the point in the input signal characteristic marked by the same number (without apostrophe).
• Switch-off voltage at point F (G) is the hysteresis voltage. This hysteresis makes it possible to always generate a clear output signal and to exclude intermediate values of the output signal (no bouncing of the output signal if the input signal changes only slowly).
• An RC low-pass filter is preferably provided in front of inputs 1, 2. This protects the other parts of the circuit against short overvoltage pulses, especially with steep slopes. In addition, this causes interference signal suppression in the case of short interference pulses. Further protective circuits are possible.
• the input circuit shown in FIG. 2 has some changes compared to the input circuit shown in FIG. 1.
• the same components are provided with the same reference numbers in FIGS. 1 and 2.
• a Zener diode 15 is arranged in resistors 13, 14.
• Another Zener diode 16 is provided between the gate electrode of transistor 5 and the anode of luminescent diode 10. So that the Zener diode 16 is supplied with current, is between the source and gate electrodes of the transistor 5
• Transistor 11 is turned on, and is part of the constant current through the luminescent diode of the optocoupler 10. In parallel with the luminescent diode of the optocoupler, there is the resistor 20, which leads the leakage currents past the luminescent diode.
• the drain electrode of transistor 6 is connected to the source electrode of transistor 5 via a further resistor 19.
• the Zener diodes 15, 16 are provided to reduce the influence of the Sohwell voltage tolerances of the transistors 5, 11 on the current-voltage characteristic and act independently of one another.
• the Zener diode 15 blocks until the voltage across the resistors 13, 14 has exceeded the Zener voltage. In this case, when the voltage continues to rise, a certain current flows through the resistor 12, which creates a potential at the gate electrode of the transistor 6. If this reaches the threshold voltage, the switch-on voltage is reached and the transistor 11 begins to conduct. A deviation in the gate threshold voltage has less of an effect on the switch-on voltage than would be the case if the Zener diode were missing.
• the input circuit shown in FIG. 4 corresponds to the input circuit according to FIG. 2 except for slight modifications.
• the same components are given the same reference numbers in FIGS. 2 and 4.
• the additional properties are achieved independently of one another and regardless of the configuration according to FIG. 2.
• Zener diode 21 In addition to the components of the input circuit according to FIG. 2, in the input circuit shown in FIG. 4 there is a Zener diode 21 between the Anode of the luminescent diode 10 and the input 2 arranged.
• the Zener diode 21 influences the current-voltage characteristic of the input circuit by limiting the maximum input current to a certain value. This characteristic curve is shown in FIG. 5. This is achieved by the Zener diode 21, prior to the on-time point, that is to say when the transistor 11 is still blocked, the gate voltage at the transistor 6 and thus the current through the resistor 7, which then makes up the essential part of the total current. limited to the maximum.
• a resistor 22 is arranged between the source of the transistor 11 and the input 2, on which the binary output signal can be coupled out alternatively to the optocoupler in the form of a voltage.
• a capacitor 23 is arranged between the gate electrode of the transistor 11 and the input 2, which causes a delay in the jump B - C in the current-voltage characteristic.
• the input signal always becomes zero (100 times per second at 50 Hz) when there is an input signal (on signal) close to the input signal zero crossings.
• the period of the periodic zero state is not only dependent on the frequency, but also on the voltage level of the input signal, since the static switching points also apply here and these are run through at different amplitudes and at different times.
• the circuit according to FIG. 6 differs from the arrangement according to FIG. 1 in that the resistor 13, which is decisive for the positive feedback, is missing.
• the elimination of the resistor 13 results in a current-voltage characteristic without the jump, i. H. at the beginning the characteristic curve has a triangular course, in which after reaching point C during the current rise the transition to the straight line falling to point D is made.
• the transistor 5 can also be of the enhancement type. So that it is conductive when the voltage is applied, a resistor 24, shown in broken lines in FIG. 4, is arranged between the input 1 and the gate electrode.
• the circuits described above With the response voltage, which is in the lower part of the input voltage range, the circuits described above have a sufficiently high power loss for interference sensitivity and contact cleaning due to the characteristics described above. After the response, a power loss that is sufficiently high for the susceptibility to interference also occurs in the entire permissible input voltage range, but this always remains within the permissible power loss.
• the circuits do not require any special settings for the nominal voltage that occurs at the installation site for the entire input voltage range.
• FIG. 7 shows a variant of the input circuit with a characteristic curve similar to that of FIG. 5.
• the same components in FIGS. 1-7 are again provided with the same reference numbers.
• the main difference to the previous circuit variants is that the second one
• Transistor 6 is replaced by a Zener diode 25.
• the gate-source Sohwell voltage of the transistor 5 drops across the resistor 19. Since this voltage also represents the gate-source voltage of transistor 5 in the case of a high-impedance transistor 1 1, the input current becomes duror even when the input voltage increases further
• Transistor 5 limited to this value (Imax). If the switch-on threshold (B) is reached while the input voltage continues to rise, then the gate-source threshold voltage is established via the resistors 13 and 14 and the Zener diode 15 at the resistor 12 and thus at the transistor 11. Transistor 11 begins to conduct. The transistor current that flows flows through the luminescence diode of the optocoupler and through resistors 9 and 19. The voltage additionally generated by this current at the relatively high-resistance resistor 9 and at the resistor 19 increases the gate-source blocking voltage of transistor 5.
• the optocoupler shown in Fig. 7 is designated 26 and contains a transistor as an output.
• the optocouplers of the other input modules are designed accordingly.

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• 1990
  • 1990-04-09 DE DE19904011415 patent/DE4011415A1/de active Granted
• 1991
  • 1991-04-08 WO PCT/EP1991/000660 patent/WO1991015775A1/de unknown

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